Wave energy recovery apparatus with power-take-off arrangement

ABSTRACT

This invention relates to a wave energy recovery apparatus with a power-take-off arrangement comprising at least a base, a reciprocating panel, two power-take-off (PTO) units with one or more generators to convert kinetic energy of waves or tidal currents to electricity, at least two gear transmissions operatively connected between the panel and the generators and at least two one-way clutch mechanisms to control the directions of rotation of the generators. The panel is arranged to rotate a half of the generators when rotating into one direction and another half of the generators when rotating into the opposite direction.

This application is a Divisional of copending application Ser. No.17/059,846, filed on Nov. 30, 2020, which is the National Phase under 35U.S.C. § 371 of International Application No. PCT/FI2018/050407, filedon May 30, 2018, all of which are hereby expressly incorporated byreference into the present application.

The present invention relates to a wave energy recovery apparatus with apower-take-off arrangement as defined in the preamble of claim 1.

The wave energy recovery apparatus according to the invention is suitedvery well for instance to be used in connection with panels or flaps oressentially plate-like wing elements, later called shorter only aspanels, hinged with their lower edge to make a reciprocating movementcaused by wave energy or tidal energy of seawater as shown for examplein the U.S. Pat. No. 7,131,269 (B2). The wave energy or tidal energycollected is further converted underwater with a conversion unit forinstance to electric energy. For the sake of simplicity, only the termwave energy is later mentioned when both the wave energy and the tidalenergy of seawater are meant.

According to prior art there are various types of wave energy recoverysystems where the arrangements include a base, and, for instance, one ormore panels pivotally connected to the base to make a reciprocating oroscillating movement about a rotation axis or pivot axis in response towave forces or tidal forces as shown for example in the U.S. Pat. No.9,279,408 (B2) that presents, among other things, how to drive the waveenergy conversion system. The oscillating movement is then converted forexample to electric energy with the help of a power-take-off (PTO) unitequipped with a power-take-off (PTO) machinery comprising a generator oralike as shown for example in the Finnish patent No. FI119791B.

The PTO can also be placed inside the reciprocating structure of thewave energy recovery apparatus, for instance, inside the panel as shownfor example in the US patent publication No. US2016040647 A1, or insidethe tubular main shaft of the panel.

Commonly, in known wave energy converter systems it is difficult toefficiently transform the energy captured from the reciprocatingmovement of waves into electrical energy. For instance, thereciprocating movement of panels causes the rotors and axles of theelectric generators to undergo a bi-directional rotational movement witha stop in connection with every reversing. As a consequence, thegenerators with components connected to them are prone to fatigue andfurther to breakages. In addition, controlling of the electricgenerators that make the reciprocating movement is complicated anddifficult.

For that reason, there have been several attempts to transform thereciprocating movement of the movable element in a unidirectionalmovement of the rotor of the generator. For instance, internationalpatent publications WO2006/118482 A1, WO2011/092555 A2 and WO2011/126451A1 present different solutions to change the reciprocating movementcaused by waves into a unidirectional movement of the rotor of thegenerator when recovering wave energy.

All these solutions of the WO publications mentioned above use at leasttwo one-way clutches, freewheels or other anti-reverse mechanisms foreach generator, which are continuously engaged and disengaged to ensurethat the reciprocating movement caused by waves is changed to aunidirectional movement of the rotor of the generator. However, thecontinuous engagement and disengagement of the one-way clutches,freewheels or other anti-reverse mechanisms mentioned above causemechanical wear and failures in the PTO systems. In addition, the PTOstructures of the solutions of these WO publications are extremelycomplicated, which also cause the PTO structures to be prone tomechanical wear that reduces the lifetime of the solutions of these WOpublications. Therefore, there is still a need for more efficient and/ormore robust PTO systems.

The object of the present invention is to eliminate the drawbacksdescribed above and to achieve a reliable, compact, economical andefficient wave energy recovery apparatus with an improved power-take-off(PTO) arrangement in order to be able to capture a maximum amount ofavailable wave or tidal energy and which apparatus is easilycontrollable. Another object of the present invention is to make theinstallation, maintenance and repairs of the wave energy conversionapparatus easy and fast, and to make it possible to easilydisconnect/connect the electric generators from/to the other structurewithout disturbing the functions of the other structure. Thus, forexample one generator can be removed and replaced with another generatorwithout disturbing the whole system. The wave energy recovery apparatuswith a power-take-off arrangement according to the invention ischaracterized by what is presented in the characterization part of claim1. Other embodiments of the invention are characterized by what ispresented in the other claims.

An aspect of the invention is to provide a wave energy recoveryapparatus with a power-take-off arrangement comprising at least a base,a reciprocating panel, two power-take-off (PTO) units with one or moregenerators to convert kinetic energy of waves or tidal currents toelectricity, at least two gear transmissions and at least two one-wayclutch mechanisms, all operatively connected between the panel and thegenerators. Advantageously, the panel is arranged to rotate a half ofthe generators when the panel is rotating into one direction and anotherhalf of the generators when the panel is rotating into the oppositedirection. Advantageously, the direction of rotation of each generatoris controlled with one one-way clutch mechanism, which one-way clutchmechanism is preferably arranged to allow the generator to have only onedirection of rotation.

The solution of the invention has significant advantages over thesolutions of the prior art. The number of relatively small PTO unitsand/or electric generators make it possible to place several PTO unitsand/or generators along the shaft of the reciprocating panel. Thisallows a torque induced stress range to be more evenly distributed alongthe panel thus reducing the peak stress range induced by the PTO torqueand thus increasing the fatigue life of the panel. That also allows thereduction in the size of the PTO components and thus the reduction incosts. The small size of the PTO units and/or generators also makes itpossible to incorporate the PTO units and/or generators into the panel.With the help of a one-way clutch, such as a sprag clutch, one or moregenerators can be arranged to rotate to one direction only and anotherone or more generators can be arranged to rotate to the oppositedirection only. Thus, a first half of the generators rotates all thetime in one direction, i.e. clockwise, and a second half of thegenerators rotates all the time in opposite direction, i.e. counterclockwise. Yet one advantage is that the arrangement comprises at leasttwo PTO units with generators. In that case, the PTO units can be takenseparately to service and changed if necessary. Yet one advantage isthat the PTO units can be installed on both sides of the panel.

In the following, the invention will be described in detail by the aidof examples by referring to the attached simplified and diagrammaticdrawings, wherein

FIG. 1 presents a simplified oblique top view of a wave energy recoveryapparatus according to the invention equipped with a reciprocatingpanel,

FIG. 2 presents in a side view and in a simplified and diagrammatic waya lower part of the wave energy recovery apparatus according to FIG. 1 atubular shaft of the panel cross-sectioned,

FIG. 3 presents a simplified oblique top view of another wave energyrecovery apparatus according to the invention,

FIG. 4 presents in a side view and in a simplified and diagrammatic waya wave energy recovery apparatus according to FIG. 3 with the lowerpart, comprising a tubular shaft, cross-sectioned,

FIG. 5 presents in a side view, enlarged and in a simplified anddiagrammatic way and cross-sectioned a power take-off unit (PTO) whichcan be used in the wave energy recovery apparatus according to theinvention,

FIG. 6 presents in a side view and in a simplified and diagrammatic wayyet another type of wave energy recovery apparatus according to theinvention,

FIG. 7 presents in a side view and in a simplified and diagrammatic waythe reciprocating panel with generators of the arrangement according toFIG. 6 ,

FIG. 8 presents in a side view and in a simplified and diagrammatic waythe motionless lower part of the arrangement according to FIG. 6 ,

FIG. 9 presents in a top view and in a simplified and diagrammatic wayand partially cross-sectioned the wave recovery arrangement according toFIG. 6 ,

FIG. 10 presents in a simplified and diagrammatic way the wave recoveryarrangement according to FIG. 6 seen cross-sectioned along the line A-Ain FIG. 9 ,

FIG. 11 presents in a side view and in a simplified and diagrammatic wayyet another type of wave energy recovery apparatus according to theinvention, a protective housing removed from the first PTO unit,

FIG. 12 presents in a side view, enlarged, in a simplified anddiagrammatic way and a power take-off unit (PTO) of the wave energyrecovery apparatus according to FIG. 11 without the protective housing,

FIG. 13 presents in a front view and in a simplified and diagrammaticway and partially cross-sectioned the power take-off unit (PTO) of thewave energy recovery apparatus according to FIG. 11 ,

FIG. 14 presents in a front view and in a simplified and diagrammaticway and a gear rim of the power take-off unit (PTO) of the wave energyrecovery apparatus according to FIG. 11 , and

FIG. 15 presents in a front view and in a simplified and diagrammaticway and a one-way clutch mechanism of the power take-off unit (PTO) ofthe wave energy recovery apparatus according to FIG. 11 .

The basic idea of the present invention is to achieve an arrangement,which comprises at least a reciprocating panel 2 hinged with its loweredge, and at least two power take-off (PTO) units 6 with theirgenerators 14. Advantageously, the PTO units 6 or at least theirgenerators 14 are relatively small. In addition, each generator 14 isarranged to rotate only to one direction, either clockwise orcounterclockwise. Preferably, the arrangement comprises an even numberof generators 14 of which a half rotates clockwise, and another halfrotates counterclockwise when seen from the same direction. At minimumthe arrangement comprises two generators 14 but the number of generatorscan be also bigger.

FIGS. 1-2 present a first advantageous embodiment of the wave energyrecovery apparatus according to the invention. In FIG. 1 the wave energyrecovery apparatus according to the invention equipped with a hingedreciprocating panel 2 is presented in a simplified oblique top view, andin FIG. 2 the wave energy recovery apparatus according to FIG. 1 ispresented in a side view and in a simplified and diagrammatic way with atubular shaft 4 of the panel 2 cross-sectioned.

The wave energy recovery apparatus comprises at least a base 1, thehinged panel 2 reciprocating about the center axis of its pivot shaftthat comprises a tubular shaft 4, fitted with bearings at both ends inbearing housings 3 that are fastened to the base 1. One bearing housing3 is at each end of the panel 2. The power-take-off (PTO) units 6 areplaced inside the tubular shaft 4, one at each end of the tubular shaft4. Rotation axes 12 of the generators of the PTO units 6 are fitted withbearings between support elements 7 in the bearing housings 3 and anintermediate support 3 c that is inside and in the middle of the tubularshaft 4. The first PTO unit 6 is fitted between the first supportelement 7 and the first side of the intermediate support 3 c, and thesecond PTO unit 6 is fitted between the second support element 7 and thesecond side of the intermediate support 3 c. The panel 2 is fastened tothe tubular shaft 4. The reciprocating motion or shorter only the motionof the panel 2 and the tubular shaft 4 is a back and forth rotatingmotion around the center axis of the tubular shaft 4. Preferably, therotation angle of the panel 2 is at maximum ±90° from the verticalposition. A transmission line 5 is used to transmit the producedelectricity to further use.

The reciprocating panel 2 oscillates on the base 1 back and forth withthe movement of seawater for recovering kinetic energy like wave energyof seawater. The panel 2 and the tubular shaft 4 rotate back and forthtogether simultaneously and at the same speed of rotation. At theproduction site the base 1 is preferably mounted onto the bottom of thesea, but it can also be near the bottom supported by pillars.

FIGS. 3-4 present another advantageous embodiment of the wave energyrecovery apparatus according to the invention. In FIG. 3 the wave energyrecovery apparatus according to the invention is presented in asimplified oblique top view, and in FIG. 4 the wave energy recoveryapparatus according to FIG. 3 is presented in a side view and in asimplified and diagrammatic way, and the lower part that comprises atubular shaft 4 is cross-sectioned.

The wave energy recovery apparatus comprises at least a base 1, a hingedpanel 2 reciprocating about the center axis of its pivot shaft thatcomprises two substantially coaxial tubular shafts 4, fitted withbearings at both ends in bearing housings 3 that are fastened to thebase 1. The panel 2 is fastened to the tubular shafts 4. One bearinghousing 3 is at each end of the panel 2 and the third bearing housing 3is in the middle of the panel 2 where the panel 2 has a recess 2 a forthe bearing housing 3. The power-take-off (PTO) units 6 are placedinside the tubular shafts 4. The reciprocating motion or shorter onlymotion of the panel 2 and the tubular shafts 4 is a back and forthrotating motion around the center axis of the tubular shafts 4. Atransmission line 5 is used to transmit the produced electricity tofurther use.

The reciprocating panel 2 oscillates on the base 1 back and forth withthe movement of seawater for recovering kinetic energy like wave energyof seawater. The panel 2 and the tubular shafts 4 rotate back and forthtogether simultaneously and at the same speed of rotation. At theproduction site the base 1 is preferably mounted onto the bottom of thesea, but it can also be near the bottom supported by pillars.

The embodiments according to FIGS. 1-4 comprise two coaxial PTO units 6that have been placed inside one tubular shaft 4 or two tubular shafts4, one PTO unit 6 in each shaft 4. Advantageously, the number of PTOunits 6 inside the tubular shafts 4 can be also bigger than two. Thus,the PTO units 6 can be inside their own tubular shafts 4 also 4, 6, 8,10, 12 or even more but always an even number.

FIG. 5 presents in a side view, enlarged and in a simplified,diagrammatic and a more detailed way and cross-sectioned a powertake-off unit or shorter PTO unit 6 that can be used in the wave energyrecovery apparatus according to the invention. The same kind of PTO unit6 can be used both the wave energy recovery apparatus according FIG. 1or FIG. 3 . Only the bearing arrangement between the two PTO units 6differs depending on the case.

A support element 7 with a circular cross-section is fastened inside thefirst bearing housing 3 so that the support element 7 extends withsmaller circular cross-sections towards the middlemost bearing housing 3in the middle of the panel 2. Between the inner circumference of thebearing housing 3 and the outer circumference of the support element 7there is an annular groove for a bearing 8 with which the tubular shaft4 is fitted in the bearing housing 3 at its first end. Correspondingly,the middlemost bearing housing 3 of the embodiment of FIG. 3 has in itsboth sides an annular groove 3 a for a bearing 9 with which the tubularshafts 4 are fitted in the middlemost bearing housing 3 at their secondend. A rotation axle 12 of the generator 14 is fitted with bearings 13at its both ends. At the first end of the axle 12 the bearing 13 is inits recess in the center of the support element 7 and at the second endof the axle 12 the bearing 13 is in its recess 3 b in the center of theannular groove 3 a for the bearing 9. Thus, all the bearings 8, 9 and 13are coaxial.

On the first end of the rotation axle 12 there is a speed changing gearsystem, such as a gear transmission 11 to convert the slow motion of thepanel 2 and tubular shaft 4 to a fast speed of rotation of the rotationaxle 12. Preferably, the gear transmission 11 is a planetarytransmission. The gear transmission 11 is coupled to the slowlyreciprocating tubular shaft 4 through a one-way clutch mechanism 10 sothat the rotation axle 12 rotates to one direction only, eitherclockwise or counterclockwise. In that case, the outer circumference ofthe one-way clutch mechanism 10 is fastened to the inner circumferenceof the tubular shaft 4 and the inner circumference of the one-way clutchmechanism 10 is fastened to the outer part of the gear transmission 11.Thus, the one-way clutch mechanism 10 is operatively connected betweenthe tubular shaft 4 and the gear transmission 11, which geartransmission 11 is further operatively connected between the one-wayclutch mechanism 10 and the rotation axle 12 of the generator 14.

On the middle part of the rotation axle 12 there is a rotor 16 of thegenerator 14. A stator 15 is axially at the same location and isfastened to the inner circumference of the tubular shaft 4. On thesecond end of the rotation axle 12 there is a flywheel 18 that isfastened to the rotation axle 12. Axially between the generator 14 andthe fly-wheel 18 there is a support flange 17 that is fastened to theinner circumference of the tubular shaft 4. The support flange 17 has abearing, preferably similar to the bearings 13 on which the rotationaxle 12 is fitted.

As mentioned earlier the advantageous embodiments of the wave energyrecovery apparatus according to the invention comprises two PTO units 6.For example, the embodiments of FIGS. 1 and 3 advantageously comprisescomprise two PTO units 6. FIG. 5 presents the first PTO unit 6 of thetwo. The second PTO unit 6 is otherwise similar to the first one but thesecond one is like a mirror image and the generator 14 inside thetubular shaft 4 is arranged to rotate to the opposite direction comparedto the generator 14 of the first PTO unit 6. In that case, the one-wayclutch mechanism 10 of the second PTO unit 6 is arranged to workreversely compared to the one-way clutch mechanism 10 of the first PTOunit 6, when seen at the same direction.

Thus, when the rotational movement of the panel 2 and the tubular shaft4 is towards the first direction, say clockwise, the one-way clutchmechanism 10 of the first PTO unit 6 is in the working mode and the geartransmission 11 of the first PTO unit 6 rotates its rotation axle 12 inthe clockwise direction, whereas the one-way clutch mechanism 10 of thesecond PTO unit 6 is in the free mode and the gear transmission 11 ofthe second PTO unit 6 neither rotates nor decelerates its rotation axle12. However, the rotation axle 12 of the second PTO unit 6 continues itsrotation by the contribution of the flywheel 18.

And, when the panel 2 goes back and the rotational movement of the panel2 and the tubular shaft 4 is towards the second direction, saycounterclockwise, the one-way clutch mechanism 10 of the first PTO unit6 is in the free mode and the gear transmission 11 of the first PTO unit6 neither rotates nor decelerates its rotation axle 12. But also now,the rotation axle 12 of the first PTO unit 6 continues its rotation bythe contribution of the flywheel 18. Whereas the one-way clutchmechanism 10 of the second PTO unit 6 is in the working mode and thegear transmission 11 of the second PTO unit 6 rotates its rotation axle12 in the counterclockwise direction. And continuing so, the rotationaxle 12 of the first PTO unit 6 rotates always clockwise and therotation axle 12 of the second PTO unit 6 rotates alwayscounterclockwise. The clockwise and counterclockwise directions arealways seen from the same direction, for example from the first end ofthe panel 2.

When the apparatus comprises only two PTO units 6 the tubular shaft 4can also be a continuous unbroken shaft with one PTO unit 6 at its bothends, as is presented in FIGS. 1 and 2 . Then the middlemost bearinghousing 3 c is totally inside the tubular shaft 4 and rotates with thetubular shaft 4. When the apparatus comprises more than two PTO units 6it is realistic that each PTO unit 6 is inside its own tubular shaft 4.

FIGS. 6-10 present a third advantageous embodiment of the wave energyrecovery apparatus according to the invention. In FIG. 6 another type ofan arrangement according to the invention is presented in a side viewand in a simplified and diagrammatic way. FIG. 7 presents in a side viewand in a simplified and diagrammatic way the reciprocating panel 2 withgenerators 14 according to the arrangement of FIG. 6 . FIG. 8 presentsin a side view and in a simplified and diagrammatic way the motionlesslower part 19 of the arrangement according to FIG. 6 , whereas FIG. 9presents in a top view and in a simplified and diagrammatic way andpartially cross-sectioned the wave recovery arrangement according toFIG. 6 , and FIG. 10 presents in a simplified and diagrammatic way thewave recovery arrangement according to FIG. 6 seen cross-sectioned alongthe line A-A in FIG. 9 .

The third embodiment of the wave energy recovery apparatus according tothe invention comprises a reciprocating hinged panel 2 that issubstantially similar to the panel 2 presented in FIG. 1 . The panel isfitted at its ends with bearings that are in bearing housings 3 locatedat the ends of the panel 2. The bearing housings 3 are fastened to thebase 1. The panel 2 has a downwards opening recess 2 b that is almost aswide as the panel 2. The recess 2 b makes room for the motionless lowerpart 19 of the arrangement. Thus, the panel 2 is able to make areciprocating rotational motion partially around the motionless lowerpart 19.

The arrangement according to third embodiment of the invention comprisessix generators 14 that are fastened to the lower edge of the panel 2with fastening elements 23. Again, the generators 14 may be more or lessthan six but, however, always an even number, for example 2, 4, 8, 10,12 or even more. Preferably, the first half of the generators 14 arefastened to the first side of the panel 2 and the second half of thegenerators 14 are fastened to the second side of the same panel 2.

Advantageously, all the generators 14 are substantially similar. Inaddition to characteristic components, each generator 14 comprises agearwheel 24 of relatively small diameter and a one-way clutch mechanism10, which both are mounted on the same axle. The one-way clutchmechanism 10 is operatively coupled between the generator axle and thegearwheel 24 axle and is arranged to allow the generator axle to rotateonly to one direction, either clockwise or counterclockwise. Inaddition, the generators 14 on the first side of the panel 2 are inreverse direction compared to the generators 14 on the second side ofthe panel 2. Thus, when gearwheels 24 of the generators 14 on the firstside of the panel 2 are directed towards the second end of the panel 2the gearwheels 24 of the generators 14 on the second side of the panel 2are directed towards the first end of the panel 2. In that case, thereis more room to arrange the gear assembly. For the sake of clarity onlyfour generators 14 are presented in FIG. 7 .

FIG. 8 presents in a side view and in a simplified and diagrammatic waythe motionless lower part 19 of the arrangement according to FIG. 6 .The lower part 19 comprises a tubular shaft 20 that is supported andfastened to the base 1 with support legs 21. The tubular shaft 20comprises on its outer circumference a number of motionless gear rims22, in this case six substantially similar gear rims 22, one for eachgenerator 14. The gear rims 22 are arranged to mesh with the gearwheels24 of the generators. The gear rims 22 and the gearwheels 24 meshingwith each other form a gear transmission 11 a for the generators 14 ofthe third embodiment of the invention.

The diameter of the gear rims 22 is relatively big compared to thediameter of the gearwheels 24. Therefore, the transmission ratio betweenthe gear rim 22 and the gearwheel 24 is relatively great. For example,the transmission ratio is greater than 10, suitably greater than 50 andpreferably greater than 100. The greater the transmission ratio thefaster the generators 14 rotate when the panel 2 makes its relativelyslow reciprocating motion. FIG. 11-15 present a fourth advantageousembodiment of the wave energy recovery apparatus according to theinvention. In FIG. 11 yet another type of an arrangement according tothe invention is presented in a side view and in a simplified anddiagrammatic way. A protective housing 25 is removed from the first PTOunit 6. FIG. 12 presents in a side view, enlarged, and in a simplifiedand diagrammatic way the first power take-off unit (PTO) 6 of the waveenergy recovery apparatus according to FIG. 11 . Whereas FIG. 13presents in a front view and in a simplified and diagrammatic way thepower take-off unit (PTO) 6 of the wave energy recovery apparatusaccording to FIG. 11 . The figure is partially cross-sectioned so thatonly the tubular shaft 4 of the panel 2 is cross-sectioned. The actualPTO unit 6 is not necessarily cross-sectioned though it hascross-sectional lines. The cross-sectional lines are only presented tomake the figure and its components easier to understand and to separatefrom each other. Correspondingly, FIG. 14 presents in a front view andin a simplified and diagrammatic way a gear rim 26 of the PTO unit 6 ofthe wave energy recovery apparatus according to FIG. 11 , and finallyFIG. 15 presents in a front view and in a simplified and diagrammaticway a one-way clutch mechanism 10 of the PTO unit 6 of the wave energyrecovery apparatus according to FIG. 11 .

The fourth embodiment of the wave energy recovery apparatus according tothe invention comprises a reciprocating hinged panel 2 that issubstantially like the panel 2 presented in FIGS. 1 and 3 . The panel 2has a hinged tubular shaft 4 that is fastened to the lower edge of thepanel 2 and is arranged to rotate along with the panel 2. The tubularshaft 4 is fitted at its ends with bearings that are inside bearinghousings 3 located at the ends of the panel 2. The bearing housings 3are fastened to the base 1. The tubular shaft 4 acts as a pivot shaftfor the reciprocating motion of the panel 2.

Preferably, the fourth embodiment of the invention comprises at leasttwo PTO units 6, one at each end of the tubular shaft 4, which endsextend outwards from the bearing housings 3. Each PTO unit 6 comprises aone-way clutch mechanism 10, a gear rim 26 having a toothed outercircumference and a similar group of generators 14 coupled to the gearrim 26 through gearwheels 24 that mesh with the gear rim 26. The gearrim 26 and the gearwheels 24 meshing with each other form a geartransmission 11 b for the generators 14 of the fourth embodiment of theinvention. Each PTO unit 6 is coupled to the tubular shaft 4 through theone-way clutch mechanism 10 so that the one-way clutch mechanism 10 isoperatively connected between the tubular shaft 4 and the innercircumference of the gear rim 26 of the gear transmission 11 b.

The gear rim 26 comprises an outer ring 27 with the toothed outercircumference, an inner ring 28 and an elastomer ring 29 between theouter and inner rings. All the rings are coaxial. The purpose of theelastomer ring 29 is to make the movements of the gear rim 26 softer andmore flexible. Depending on local sea conditions the elastomer ring 29may not be needed. In that case, neither the inner ring is needed.However, the gear rim 26 with or without the inner ring 28 is relativelybig in its diameter and it is also relatively heavy. The mass isconcentrated near the outer circumference of the gear rim 26, whichmeans that the gear rim 26 has a high inertia. Thus, the gear rim 26 hasproperties of a flywheel and therefore it is arranged to act as aflywheel at the same time when it acts as the gear rim.

The one-way clutch mechanism 10 can be any type of a one-way clutch,preferably the one-way clutch mechanism 10 is a so-called sprag clutchthat has an outer ring 30, an inner ring 31 and an active ring 32between the outer and inner ring. The active ring 32 comprises spragsthat allow the rings 30 and 31 to rotate relative to each other into onedirection but lock the rotation into the opposite direction.

The one-way clutch mechanism 10 is fastened with its inner ring 31 ontothe tubular shaft 4 to rotate along with the tubular shaft 4. The innerring 31 rotates with the tubular shaft 4 at the same time, to the samedirection and at the same speed. The outer ring 30 of the one-way clutchmechanism 10 is fastened to the inner circumference of the inner ring 28of the gear rim 26 or directly to the inner circumference of the gearrim 26 if the elastomer ring 29 is not used. Thus, the one-way clutchmechanism 10 is arranged to allow the gear rim 26 to rotate only intoone direction regardless of the direction of rotation of the tubularshaft 4.

The diameter of the gear rim 26 is relatively big compared to thediameter of the gearwheels 24. Therefore, the transmission ratio betweenthe gear rim 26 and the gearwheels 24 is relatively great. For example,the transmission ratio is greater than 10, suitably greater than 50 andpreferably greater than 100. The greater the transmission ratio thefaster the generators 14 rotate when the panel 2 makes its relativelyslow reciprocating motion.

The arrangement according to fourth embodiment of the inventioncomprises two PTO units 6 with a group of generators 14 in each PTO unit6. Now, the generators 14 are presented eight in each PTO unit 6, butagain, the generators 14 may be more or less than eight; however, alwaysan even number, for example 2, 4, 6, 10, 12 or even more.

When the rotational movement of the panel 2 and the tubular shaft 4 istowards the first direction, say clockwise, the one-way clutch mechanism10 of the first PTO unit 6 is in the working mode and the gear rim 26 ofthe first PTO unit 6 rotates the generators 14 of the first PTO unit 6,whereas the one-way clutch mechanism 10 of the second PTO unit 6 is inthe free mode and the gear rim 26 of the second PTO unit 6 neitherrotates nor decelerates the generators 14 of the second PTO unit 6 but,however, the rotation of the generators 14 of the second PTO unit 6continues by the contribution of the flywheel effect of the gear rim 26.

And, when the panel 2 goes back and the rotational movement of the panel2 and the tubular shaft 4 is towards the second direction, saycounterclockwise, the one-way clutch mechanism 10 of the first PTO unit6 is in the free mode and the gear rim 26 of the first PTO unit 6neither rotates nor decelerates the generators 14 of the first PTO unit6. But also now, the rotation of the generators 14 of the first PTO unit6 continues by the contribution of the flywheel effect of the gear rim26, whereas the one-way clutch mechanism 10 of the second PTO unit 6 isin the working mode and the gear rim 26 of the second PTO unit 6 rotatesthe generators 14 of the second PTO unit 6.

It is common to all the embodiments of the invention that thearrangement comprises at least two PTO units 6 that each may compriseone or more generators 14. Also, the generators are relatively small insize and arranged to be rotated fast by different types of geartransmissions. For example, when the generators 14 are rotated through agear transmission the transmission ratio is greater than 10, suitablygreater than 50 and preferably greater than 100. The greater thetransmission ratio the faster the generators 14 rotate when the panel 2makes its relatively slow reciprocating motion.

Further in common is that a half of the generators 14 are rotated onlyto one direction and another half of the generators 14 are rotated onlyto the opposite direction. In that case, seen from the same directionthe first half of the generators 14 are rotated, for example, clockwiseand the second half of the generators 14 are rotated counterclockwise,or vice versa. Thus, the first half of the generators 14 are rotatedwhen the panel 2 makes its reciprocating movement to the first directionand the second half of the generators 14 are rotated when the panel 2makes its reciprocating movement to the second direction that isopposite to the movement of the first direction. This kind of operationis arranged by the use of one-way clutch mechanisms 10 that are placedbetween the movement of the panel 2 and the rotation of the axles of thegenerators 14.

It is obvious to the person skilled in the art that the invention is notrestricted to the examples described above but that it may be variedwithin the scope of the claims presented below. Thus, for example, thestructure and positions of the PTO unit can be different from what ispresented.

The invention claimed is:
 1. Wave energy recovery apparatus with apower-take-off arrangement comprising at least a base, a reciprocatingpanel, two power-take-off (PTO) units with each PTO unit comprising oneor more generators to convert kinetic energy of waves or tidal currentsto electricity, at least two gear transmissions and at least two one-wayclutch mechanisms where the gear transmissions and one-way clutchmechanisms are operatively connected between the panel and thegenerators, wherein the panel is arranged to rotate a half of thegenerators when the panel is rotating into one direction and anotherhalf of the generators when the panel is rotating into the oppositedirection, wherein the apparatus comprises a hinged tubular shaft thatis fastened to the lower edge of the panel and is arranged to rotatealong with the panel, and the apparatus comprises two or more PTO unitscoupled to the tubular shaft, each PTO unit comprising a similar groupof generators, a gear transmission for its generators and a one-wayclutch mechanism operatively connected between the tubular shaft and thegear transmission.
 2. Wave energy recovery apparatus according to claim1, wherein the direction of rotation of each generator is controlledwith one one-way clutch mechanism.
 3. Wave energy recovery apparatusaccording to claim 1, wherein the one-way clutch mechanism is arrangedto allow the generator to have only one direction of rotation.
 4. Waveenergy recovery apparatus according to claim 1, wherein each geartransmission is equipped with a transmission ratio effecting between therotational movement of the panel and the rotation axle of the generator,which transmission ratio is greater than
 10. 5. Wave energy recoveryapparatus according to claim 1, wherein the PTO units are equipped withflywheel properties to maintain the rotation of the axle of thegenerator when the generator is rotating freely.
 6. Wave energy recoveryapparatus according to claim 1, wherein the gear transmission comprisesa gear rim meshing with gearwheels of the generators that are radiallyplaced on the outer circumference of the gear rim.
 7. Wave energyrecovery apparatus according to claim 1, wherein the one-way clutchmechanism operatively connected between the tubular shaft and the geartransmission.
 8. Wave energy recovery apparatus according to claim 1,wherein the one-way clutch mechanism is a sprag clutch.
 9. Wave energyrecovery apparatus according to claim 2, wherein the one-way clutchmechanism is arranged to allow the generator to have only one directionof rotation.
 10. Wave energy recovery apparatus according to claim 2,wherein each gear transmission is equipped with a transmission ratioeffecting between the rotational movement of the panel and the rotationaxle of the generator, which transmission ratio is greater than
 10. 11.Wave energy recovery apparatus according to claim 3, wherein each geartransmission is equipped with a transmission ratio effecting between therotational movement of the panel and the rotation axle of the generator,which transmission ratio is greater than
 10. 12. Wave energy recoveryapparatus according to claim 2, wherein the PTO units are equipped withflywheel properties to maintain the rotation of the axle of thegenerator when the generator is rotating freely.